The present invention relates to a network system in which a plurality of terminal devices are connected via channels to an ATM switching equipment, and to a method of setting a call between the terminal devices in this network system.
SVC (Switched Virtual Connection) service has been introduced into the field of ATM (Asynchronous Transfer Mode) communications in recent years. The "SVC service" is offered to enhance a flexibility of the service by connecting the terminal devices constituting the network system to other arbitrary terminal devices at arbitrary timings at arbitrary speeds. The SVC service is actualized by performing a protocol prescribed in an ATM forum as well as in ITU (International Telecommunication Union).
There arises, however, the following problem inherent in the ATM network system when setting an SVC connection (based on the SVC service) in accordance with the protocol prescribed at the present. FIG. 33 is a diagram showing an example of a construction of the ATM network system. Referring to FIG. 33, the ATM network system is constructed of an ATM switch (ATM-SW) 1, and ATM terminal devices (terminals) 2, 3. The ATM switch 1 and the terminals 2, 3 respectively include UNIs (User Network Interfaces) 4 for mutually connecting the ATM switch 1 to the terminal 2 or 3, signaling processing units 5a14 5c for actualizing the above-described SVC service, and ILMI (Interim Local Management Interface) units 6a-6c for controlling a management function over the ATM switch 1 and the terminals 2, 3. Then, each signaling processing unit 5a executes a signaling protocol pursuant to the ATM forum or the ITU.
By the way, in the prior art ATM network systems, the signaling protocols are not unified in some cases in the system as a whole. For example, in the constructive example illustrated in FIG. 33, the signaling processing unit 5a of the terminal 2 is set to perform a signaling procedure (which is a message exchange for carrying out the call setting) on the basis of the signaling protocol pursuant to the ATM forum, while the signaling processing unit 5b of the ATM switch 1 and the signaling processing unit 5c of the terminal 3, are set to effect the signaling procedure on the basis of a signaling protocol (ITU-T recommendation Q.2931). If there are differences in terms of the signaling protocols pursuant thereto between the ATM switch 1, terminal 2 and the terminal 3, however, the call can not be set between the terminal 2 and the terminal 3 in some cases due to the difference in the standards. Referring to FIG. 34, there will be given an explanation of the way the call is unable to set.
FIG. 34 is a sequence diagram showing a signaling procedure when setting the call between the terminals 2 and 3 in the ATM network system illustrated in FIG. 33. Referring again to FIG. 34, when the terminal 2 sets the call with respect to the terminal 3, a signaling processing unit 5a of the terminal 2 transmits "SETUP" defined as a message for setting the call to an ATM switch 1. When the ATM switch 1 receives "SETUP", a signaling processing unit 5b of the ATM switch 1 transmits "SETUP" to the terminal 3. Subsequently, the signaling processing unit 5b of the ATM switch 1 transmits "CALL-PROC" defined as a message for accepting the call setting message "SETUP" to the terminal 2. The terminal 2, upon receiving this message "CALL-FPROC", makes a T310 timer start counting based on the signaling protocol pursuant to the ATM forum, and there must be a wait-for-receipt status of "CONN" defined as a response message to "SETUP". On the other hand, when the terminal 3 receives "SETUP" from the ATM switch, 1, a signaling processing unit 5c of the terminal 3 transmits "ALERT" defined as a call-out message based on the signaling protocol pursuant to the ITU to the ATM switch 1, and subsequently transmits "CONN" to the ATM switch 1. Herein, the signaling protocol pursuant to the ATM forum is prescribed so that the terminal receiving "SETUP" transmits "CONN" without transmitting "ALERT". Therefore, a counting time of the T310 timer in the terminal 2 is set assuming a time till "CONN" transmitted from the call-in terminal (the terminal 3) is received since the call-out terminal (the terminal 2) transmitting "SETUP" has received "CALL-PROC".
As explained above, however, the terminal 3, upon receiving "SETUP" transmits "CONN" after transmitting "ALERT". Hence, it follows that the terminal 2 receives "CONN" in delay of a time till the terminal 3 transmits "CONN" since it has transmitted "ALERT". As a result, the T310 timer is timed out before the terminal 2 receives "CONN" from the ATM switch 1 in some cases. Furthermore, if the T310 timer is timed out, the terminal 2 executes the processing on the assumption that the call can not be set with respect to the terminal 3 even when receiving "CONN" thereafter.
Further, the signaling protocol based on UNI specifications of an ATM forum is classified in-to a version 3.0 (hereinafter abbreviated to "V3.0"), a version 3.1 (hereinafter abbreviated to "V.1") and a version 4.0 (hereinafter abbreviated to "4.0"), which all have different contents. FIGS. 35 and 36 are diagrams showing a difference between the signaling protocols V3.0 and V3.1. FIG. 35(a) is a diagram showing parameter elements of an AAL (ATM Adaptation Layer) of "SETUP" in V3.0. FIG. 35(b) is a diagram showing AAL parameter elements of "SETUP" in V3.1. Further, FIG. 36(a) is a diagram showing information elements of broadband high-order layer information (B-HLI) of "SETUP" in V3.0. FIG. 36(b) is a diagram showing information elements of the broadband high-order layer information of "SETUP" in V.3.1. Moreover, FIG. 36(c) is a diagram showing QOS (Quality of Service) parameter elements of "SETUP" in V.3.0. FIG. 36(d) is a diagram showing QOS parameter elements of "SETUP" in V.3.1. As shown in FIGS. 35(a) and 35(b), the AAL parameter elements of "SETUP" have one more octet in V3.1 than in V3.0. More specifically, they have an octet 11.2 defined in V3.1, which does not exist in V3.0. Note that the AAL is defined as a protocol for treating functions depending on the SVC service. Further, a content of the information element of the octet 11 in V3.0 is different from that in V3.1. Note that "Structured Data Transfer" in FIG. 35(a) literally indicates a structured data transfer, while "Structured Data Transfer Blocksize" literally shows a block size of a structured data transfer CBR (fixed speed) service. Moreover, as shown in FIGS. 36(a) and 36(b), with respect to the information elements of the broadband high-order layer information (B-HLI) of "SETUP", "High layer profile" existing in the definition of "High layer information type (octet 5)" in V3.0 is deleted in V3.1. Further, as shown in FIGS. 36(c) and 36(d), with respect to the QOS parameter elements of "SETUP", ITU-T which is not seen in V3.0 is added to the definition of "QOS Class Forward (octet 5)" and "QOS Class Backward (octet 6)" in V3.1. Note that a concrete parameter of ITU-T is written posterior to an octet 7.
As described above, the content of the signaling protocol (e.g., "SETUP") pursuant to the ATM forum differs depending on the versions, and hence, for example, even if the respective processing units 5a-5c of the ATM switch 1 and the terminals 2, 3 illustrated in FIG. 33 are based on the signaling protocols pursuant to the ATM forum, the call could not be set in some cases between the terminal 2 and the terminal 3 in the case of the versions being different.